1. Field of the Invention
The present invention relates generally to footwear, and more particularly to a shoe sole having a resilient insert to provide cushioning and support to the foot, wherein the insert is constructed to reduce or eliminate the production of undesirable noises within the components of the shoe sole as a force is applied thereto.
2. Background Art
Over the last century, shoe manufacturers have sought to develop a shoe which strikes a balance between cushioning and support. Throughout the course of an average day, the feet and legs are subjected to substantial impact forces. Running, jumping, walking and even standing exert forces upon the feet, legs and joints which can lead to discomfort, fatigue and injury.
Remarkably, the anatomy of the human foot is capable of withstanding and dissipating substantial impact forces. The natural fat pads of the heel and forefoot, as well as the spring-like flexibility of the longitudinal and transverse arches, help to cushion and absorb impact forces applied to the foot. Equally important, the structure of the foot transfers the absorbed forces to the legs and associated muscles as energy, to facilitate locomotion. For example, when walking or running, the Achilles tendon and arches of the foot stretch and contract to transfer and store energy (i.e., the absorbed impact forces) in the tendons and ligaments of the foot and leg. As the contractions are released, the energy stored in the tendons and ligaments is also released to power the stride or gait and to reduce the xe2x80x9cworkxe2x80x9d assumed by the muscles of the leg.
While the anatomy of the foot possesses natural cushioning and energy-absorbing and energy-transferring characteristics, the foot and leg alone cannot effectively handle many of the forces applied to the foot while engaging in athletic activity. Accordingly, to avoid fatigue and injuries (such as damage to the muscles, tendons and ligaments and stress fractures to the bones), footwear which provides proper support and cushioning to the foot and leg should be worn.
Ideally, footwear should complement and work with the bio-mechanics of the foot by having a component which absorbs shock, but also possesses resiliency sufficient to avoid collapsing under the weight of the wearer (e.g., a shoe sole having an insole, midsole and outsole). Many attempts have been made to improve the cushioning, support and resiliency of a shoe sole. An article of footwear having a cushioning member disposed therein is described in International Patent Publication No. PCT/US94/00895 to Reebok International Ltd., the disclosure of which is incorporated herein in its entirety by reference. The article of footwear comprises a sole and a resilient cushioning member containing air at ambient pressure positioned within a cavity of the sole. The resilient cushioning member is blow-molded from an elastomeric material. It includes a heel chamber, a forefoot chamber, and a communication chamber which allows air to flow between the heel and forefoot chambers. The communication chamber contains impedance means (i.e., a pinched or circuitous pathway disposed within the communication chamber) to regulate the flow of air between the heel and forefoot chambers. As a force is applied to either the heel or forefoot of the sole, air within the resilient insert is transferred from one chamber to the other through the communication chamber of the insert. The impedance means disposed within the communication chamber controls the rate at which air flows between the chambers to prevent xe2x80x9cbottoming outxe2x80x9d, which would leave either chamber without sufficient air to cushion or support the heel or forefoot of the wearer.
Another shoe which incorporates a system for providing resilient support and cushioning to the foot of the wearer while standing, walking or running is described in U.S. Pat. No. 5,771,606 to Litchfield et al., the disclosure of which is also incorporated herein in its entirety by reference. U.S. Pat. No. 5,771,606 discloses a resilient insert for a shoe sole having a plurality of heel chambers, a plurality of forefoot chambers, and a centrally located passage which fluidly connects the heel and forefoot chambers of the resilient insert. The resilient insert is blow-molded from an elastomeric material and contains air at ambient pressure. It is positioned between and bonded to a midsole and an outsole. As the heel of the shoe strikes a surface, air within the resilient insert is transferred from the plurality of heel chambers to the plurality of forefoot chambers, via the centrally located passage, to provide continuous cushioning and support to the wearer.
Like the article of footwear described in the International Patent Publication No. PCT/US94/00895 above, the centrally located passage of U.S. Pat. No. 5,771,606 may contain impedance means to restrict the flow of air between the chambers to keep air from rushing out of the heel and chambers of the resilient insert. As a result, air is transferred between the chambers of the resilient insert in a controlled or regulated manner to provide sufficient support and cushioning to both the heel and forefoot portion of the shoe, as the wearer proceeds through heel strike to toe-off.
Without question, the resilient inserts discussed above provide an unparalleled balance of cushioning and support to the foot of the wearer. However, experience has shown that the disclosed inserts may produce undesirable squeaks, wheezes and breathing sounds when a force is applied thereto. The state of the molding art at the time of these inventions was such that the disclosed resilient inserts are formed using a blow-molding technique resulting in xe2x80x9cflashingsxe2x80x9d or excess edges of elastomeric material which are used as laminating areas to secure or bond the resilient inserts within the cavities of the midsoles, and to assist in the formation of segmenting channels within the interior of the heel and forefoot chambers. As a force is applied to and relieved of the shoe sole, the resilient insert recovers at a rate different than the foam which forms the midsole of the shoe. As a result, the resilient insert and midsole exert stresses on each other, which cause the components to slightly pull apart at the bonding areas. Over time, the application of impact forces to the shoe sole results in the production of friction between the resilient insert and the midsole of the shoe. This friction within the components of the shoe sole can generate an audible noise (a xe2x80x9csqueakxe2x80x9d) as the user moves, which is not desirable.
In addition, where the angles of the disclosed resilient insert are somewhat xe2x80x9cflatxe2x80x9d, the resilient insert is not necessarily permitted to sit flush against, and securely bond to, the walls of the midsole cavity or the outsole of the shoe sole. It is in these areas of potentially discontinuous bonding where further stress and friction are produced, resulting in the audible squeak mentioned above, as the wearer passes from stride to stride.
The blow-molding technique mentioned above has a further disadvantage in that the communication chamber or fluid passageway extending between the heel and forefoot chambers of the insert cannot be formed particularly small in diameter. As a result, a pinched or circuitous impedance structure is required to regulate the flow of air from one chamber to the other, similar to a conventional valve mechanism. The pinched or circuitous channel can, however, create excessive turbulence in the communication chamber or passageway. In some instances, this turbulence is audible to the wearer as a xe2x80x9cwheezingxe2x80x9d or xe2x80x9cbreathingxe2x80x9d sound.
Attempts have been made to reduce the undesirable squeaking, wheezing and breathing sounds discussed above. One such attempt involves wrapping fabric tape about the perimeter of the insert. However, while some fabric tape wrappings have successfully prevented friction and squeaking about the sides of the cushioning insert, they have not been successful in preventing friction and squeaking at other areas of the cushioning insert. Furthermore, such wrappings have no affect on reducing the wheezing or breathing sound which emanates from within the communication chamber or passage between the heel and forefoot chambers.
Accordingly, it is an object of the present invention to provide an article of footwear with a sole and resilient insert which offers cushioning and support to the structures of the foot as the user moves through the gait cycle from heel strike to toe-off.
It is a further object of the invention to provide an article of footwear with a midsole, a resilient insert, and an outsole shaped and constructed of materials which work together to absorb and transfer impact forces away from the anatomy of the foot without producing undesirable noises.
It is still another object of the invention to provide a resilient insert for a shoe with a heel chamber, a forefoot chamber, and a centrally located passageway to communicate air between the heel and forefoot chambers to support and cushion the foot, without generating an audible turbulence sound within the interior of the passageway.
The present invention solves the above stated problems by providing a shoe sole with a midsole, an outsole, and a resilient insert. The midsole is formed from a first elastomeric material and comprises a top surface, a bottom surface, and a side wall which define a first thickness. The outsole has a top surface, a bottom surface, and a side wall which define a second thickness. The resilient insert is formed from a second elastomeric material and is disposed between the bottom surface of the midsole and the top surface of the outsole. The resilient insert comprises a heel chamber, a forefoot chamber, and a passageway fluidly connecting the heel chamber and the forefoot chamber. The second elastomeric material of the resilient insert enables the resilient insert to recover at a rate similar to the rate of recovery of the midsole, to permit the resilient insert and midsole to absorb and recover from impact forces applied to the shoe sole at substantially equal rates.
In another embodiment of the invention, a shoe sole has a midsole, an outsole, and a resilient insert. The midsole is formed from a first elastomeric material and comprises a top surface, a bottom surface, and a side wall which define a first thickness. The outsole has a top surface, a bottom surface, and a side wall which define a second thickness. The resilient insert is formed from a second elastomeric material and is disposed between the bottom surface of the midsole and the top surface of the outsole. The second elastomeric material of the resilient insert enables the resilient insert to recover at a rate similar to the rate of recovery of the midsole, to permit the resilient insert and midsole to absorb and recover from impact forces applied to the shoe sole at substantially equal rates.
In yet another embodiment of the invention, a shoe sole comprises a resilient insert, an outsole and a midsole. The resilient insert has a top surface, a bottom surface, and a side wall which extends between the top surface and the bottom surface. The midsole has a top surface, a bottom surface, and a side wall which define a thickness, and a cavity defined within the bottom surface of the midsole having a top surface and a peripheral wall. The cavity of the midsole receives the resilient insert such that the side wall of the resilient insert is arranged substantially flush against the peripheral wall of the cavity to prevent the formation of gaps between the cavity and the resilient insert to reduce the production of friction and related noise.
In still another embodiment of the invention, a shoe sole comprises a midsole and an insert disposed within a cavity of the midsole. Upon application of a force to the top surface of the midsole, the midsole insert are compressed, and upon recovery from the force, shear stress between the resilient insert and the midsole is insufficient to cause relative movement between the midsole and the resilient insert.
In yet another embodiment of the invention, a method for constructing a shoe sole comprises the steps of molding a midsole from a first elastomer, forming a cavity in the midsole, molding a resilient insert from a second elastomer, inserting and bonding the resilient insert within the cavity of the midsole, and securing an outsole to the resilient insert and midsole. The elastomeric material of the resilient insert enables the resilient insert to recover at a rate similar to the rate of recovery of the midsole, to permit the resilient insert and midsole to absorb and recover from impact forces applied to the shoe sole at substantially equal rates.
In still another embodiment of the invention, a method for manufacturing a shoe sole comprises the steps of forming a foam midsole having a cavity with a depth, forming a resilient insert with a height greater than the depth of the cavity, placing the resilient insert in the cavity, and applying an adhesive to the bottom of the midsole and securing said outsole to the midsole and resilient insert placed in the cavity, wherein a bulge is formed in the top of the midsole by the force of the outsole against the resilient insert.